6-Fluoro-2-[4-(pyridin-2-yl)but-3-yn-1-yl]imidazo[1,2-a]pyridine is described in PCT patent application WO05123703 (Example 74) as a negative allosteric modulator of the metabotropic glutamate receptor 5 (mGluR5). The compound has the following structure:

The present invention is based on the discovery that the mono-phosphate of 6-fluoro-2-[4-(pyridin-2-yl)but-3-yn-1-yl]imidazo[1,2-a]pyridine exhibits surprisingly much better solubility characteristics as compared to the corresponding free base. The free base has an aqueous solubility of 0.5 mg/mL whereas the mono-phosphate salt has an aqueous solubility of 21.0 to 32.5 mg/mL, at all relevant physiological pH. Thus the increase of the solubility of at least 40 times of the mono-phosphate salt will greatly improve the pharmacological properties of the active compound.
In a first aspect, the present invention relates to the mono-phosphate salt of 6-fluoro-2-[4-(pyridin-2-yl)but-3-yn-1-yl]imidazo[1,2-a]pyridine.
In another aspect, the present invention relates to two distinct crystalline forms, Polymorph I and Polymorph II of the 6-fluoro-2-[4-(pyridin-2-yl)but-3-yn-1-yl]imidazo[1,2-a]pyridine mono-phosphate salt, respectively.
In yet another aspect, the present invention relates to the amorphous form of the 6-fluoro-2-[4-(pyridin-2-yl)but-3-yn-1-yl]imidazo[1,2-a]pyridine mono-phosphate salt.
The aforementioned salt and its crystalline and amorphous forms can be distinguished by physical and chemical properties that can be characterized by X-ray powder diffraction patterns, infrared spectra, melting behavior or glass transition temperatures.
In another aspect, the invention provides a process of preparing the Polymorph I and the Polymorph II of the 6-fluoro-2-[4-(pyridin-2-yl)but-3-yn-1-yl]imidazo[1,2-a]pyridine mono-phosphate salt.
The invention also includes pharmaceutical compositions comprising a therapeutically effective amount of a 6-fluoro-2-[4-(pyridin-2-yl)but-3-yn-1-yl]imidazo[1,2-a]pyridine mono-phosphate salt in a crystalline or in an amorphous form, together with one or more pharmaceutically acceptable carrier, diluent or excipient therefor.
In accordance with the invention the abovementioned crystalline or amorphous forms of the 6-fluoro-2-[4-(pyridin-2-yl)but-3-yn-1-yl]imidazo[1,2-a]pyridine mono-phosphate salt can be used for the preparation of medicaments useful in the control or the prevention of disorders based on the mGlu5 receptor.